As they retreat, they are met with more mockery, and Miia gets mad. Kurusu determines that while the Prohibited Matters will get her in trouble if she overreacts, there's no law against _him_ punching that asshole in the face.
(I am not a lawyer, this is not legal advice.)
Miia asks him why he did it. Kurusu replies that he couldn't let someone be cruel to a girl like that.
Miia is overjoyed that he truly sees her as a girl despite the species difference and is DTF right now. Only Smith deciding to impose on them for dinner keeps them out of jail.